Natural organic matter, such as wood, agricultural waste, algae, and a wide variety of other feedstocks can be heated in the absence of oxygen to produce pyrolysis oil. The pyrolysis oil is produced from biomass in a pyrolysis reactor, so the pyrolysis oil is a renewable resource. Pyrolysis oil can be directly used as a fuel for some applications, such as certain boilers and furnaces, and it can also serve as a feedstock for the production of fuels in petroleum refineries. Pyrolysis oil has the potential to replace petroleum as the source of a significant portion of transportation fuels.
However, pyrolysis oil is a complex, highly oxygenated organic liquid having properties that currently limit its utilization as a biofuel. For example, biomass-derived pyrolysis oil has high acidity and a low energy density attributable in large part to oxygenated hydrocarbons. These oxygenated hydrocarbons can undergo secondary reactions during storage to produce undesirable compounds, such as oligomers, polymers, and other compounds that can block liquid transport operations. As used herein, “oxygenated hydrocarbons” or “oxygenates” are organic compounds containing hydrogen, carbon, and oxygen. Such oxygenated hydrocarbons in the pyrolysis oil include carboxylic acids, phenols, cresols, alcohols, aldehydes, etc. Hydrocarbons in conventional pyrolysis oil typically include about 30 weight percent or greater oxygen, and there may be more oxygen present in the form of water or other non-hydrocarbon compounds. The pyrolysis oil is more useful as a biofuel or as a raw material for many processes if the oxygenated hydrocarbons are deoxygenated by hydroprocessing. Such deoxygenation typically produces water, carbon monoxide, and/or carbon dioxide as well as a substantially oxygen-free hydrocarbon, and the water or carbon dioxide can then be removed from the hydrocarbon fraction (which may still be referred to as pyrolysis oil.)
Unfortunately, deoxygenating pyrolysis oil necessitates heating the oil to hydroprocessing reaction temperatures. The hydroprocessing reaction temperatures result in reactions in the pyrolysis oil that typically produce solids that plug or foul the processing catalyst in a deoxygenation (or hydroprocessing) reactor. The solids form on the hot equipment and on the deoxygenation catalyst, reduce the catalytic activity, and slow or block liquid flow through the deoxygenation reactor. The solids are often a glassy brown polymer or powdery brown char, and these solids limit the deoxygenation reaction duration because the catalyst and reactor must be periodically purged of solids. In some cases, the catalyst is stuck together by the polymer, and may need to be drilled out of the reactor for removal. Furthermore, complete deoxygenation of pyrolysis oil tends to hydrogenate the aromatics in the pyrolysis oil, which lowers the octane rating of the resulting naphtha.
Accordingly, it is desirable to provide methods and apparatuses for deoxygenating pyrolysis oil without plugging, or at least with reduced plugging, of the catalyst and deoxygenation reactor. In addition, it is desirable to provide methods and apparatuses that minimize hydrogenation of the pyrolysis oil during the deoxygenation process. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawing and this background.